The invention concerns generally the structural technology of mobile telephones and similar portable electronic terminals. Especially the invention concerns the field of shielding the user interface of a mobile telephone or a similar portable terminal against electrostatic discharges and electromagnetic interference.
The user interface of mobile telephones and similar portable electronic terminals typically comprises a display, which is almost invariably an LCD (liquid crystal display) screen, and a selection of keys. In mobile telephones the user interface comprises additionally a microphone, a speaker and a buzzer for emitting ringing tones. A very widely used structural concept is to build the user interface on one side of a relatively large printed circuit board (compared to the overall size of the device) which is then covered with an outer cover to encase the user interface side of the device and to achieve a desired outer appearance.
Some kind of conductive shielding is required on top of the user interface to make sure that static charges that accumulate into the user and/or the portable terminal will not find a discharge path through the user interface into the sensitive electronic components inside the terminal. FIG. 1 is an exploded cross-sectional view that shows a known structural arrangement which is built on a PCB 101 with a number of contact pads on its upper surface. An insulating film 102 covers the PCB except of those contact pads onto which components are to be placed. The keyboard part comprises a dome sheet 103 (or alternatively a selection of individual key domes) made of some resilient material that is electrically conductive at least at the concave surface of each dome. Additionally the keyboard part comprises a rubbery keymat 104 where the bulging protrusions constitute the visible parts of the keys. A microphone 105 is coupled to its contact pad(s), and the keyboard-microphone entity is covered by an ESD shield 106 which is made of a thin sheet of stainless steel or other conductive material.
The display part comprises an LCD display unit 107 and a metallic ESD frame 108 covering it. Similarly the loudspeaker part of the structure comprises the loudspeaker proper 109 and a metallic ESD cover 110. A pair of highly elastic protective gaskets 111a and 11b are inserted on top of the outer edge of the loudspeaker part and display part respectively, and the whole user interface is covered with an outer cover 112. A transparent window 113 covers the display unit in the completed construction.
FIG. 2 is a cross-sectional view of the prior art structure shown in FIG. 1 in assembled composition. The projections that protrude downwards from the edges of the metallic ESD shields 106, 108 and 110 are bent around the edges of the PCB 101 so that they come into contact with a number of grounding pads (not shown).
Another known approach to the task of fighting ESD is to use discrete components like capacitors and ferrites on a printed circuit board to prevent the eventual ESD discharges that get coupled to certain contact pads from proceeding to the more sensitive parts of the circuitry.
The problem of the prior art arrangements is that they are relatively complicated from the viewpoint of automated assembling. It is therefore an object of the present invention to provide an ESD shielding solution for the user interface parts of a mobile telephone or a similar portable terminal that is simpler to assemble than the structure of FIGS. 1 and 2. It is an additional object of the invention that the ESD shield should allow the user interface parts to be made very thin in the direction perpendicular to the surface of the PCB.
The objects of the invention are achieved by providing an integrated display frame and ESD shield component the shielding effect of which extends over the whole user interface. Advantageously the integrated display frame and ESD shield component also constitutes a support for the gasket(s) that separate it from the device""s outer cover.
The display frame according to the invention is characterized in that it comprises a first extended portion which is elevated, perforated and thereby arranged to essentially cover a loudspeaker located in the vicinity of said display unit, and a second extended portion which is perforated and thereby arranged to essentially cover a keypad located in the vicinity of said display unit.
The invention applies also to a user interface construction for a portable terminal of a communication system, which comprises a circuit board having a first surface, a keypad, a display unit and a loudspeaker on said first surface and an outer cover arranged to essentially cover said keypad, display unit and loudspeaker. It is characterized in that it comprises between the keypad, display unit and loudspeaker and the outer cover an extended display frame which is electrically conductive, coupled to a ground potential member appearing on the circuit board and arranged to hold the keypad, display unit and loudspeaker in place with respect to the circuit board and to essentially cover the keypad, the display unit and the loudspeaker so as to protect them against electrostatic discharges.
According to the present invention, the number of separate components in the user interface structure can be reduced and the assembly phase correspondingly simplified by extending the frame of the display unit to cover also other parts of the user interface. A single structural component may act as a mechanical holder for the display screen and other user interface parts, as well as a complete ESD shield.
In a further developed embodiment of the invention the integrated ESD shield acts even as a supporting insert for the gasket(s) that are used e.g. between the display part and the outer cover and/or between the loudspeaker part and the outer cover and/or between the microphone and the outer cover. An advantageous way of manufacturing the gasket(s) is injection moulding, in which case the integrated ESD shield may be put into the mold as a so-called insert before the injection of the gasket material. The integrated ESD shield may comprise perforated portions or other specific design details in order to enhance its usability as an insert.